The present invention generally relates to a method for controlling an engine of a vehicle. More specifically, the present invention is directed to a method for calculating an air flow rate at a cylinder port, which is useful for an A/F ratio control during acceleration/deceleration driving operations of a vehicle, and furthermore to a method for calculating a throttle valve opening angle employed in a transmission control, a suspension control and the like.
In principle, according to a basic idea for a fuel supply to an engine, the fuel is injected in such a manner that a target A(air)/F(fuel) ratio is achieved with respect to an air flow rate at a cylinder port. However, it is very difficult for the present engine control technique to correctly detect such an air flow rate at the port of the cylinder, especially, during a transition driving condition.
There are the below-mentioned reasons why the correct air-flow rate calculation cannot be achieved:
(a). An air-flow rate sensor for measuring an air flow rate, in principle, does not measure the air flow rate at the cylinder port, but measure the air flow rate which passes through a portion adjacent to a throttle valve. As a result, there is a difference between these air-flow rates during the transition driving operation of the vehicle. PA1 (b). There are a flap type sensor and a hot wire (H/W) sensor as the air-flow sensor, which own a measurement lag. Although the response characteristic of the H/W sensor is superior to that of the flap type sensor, there exists a slight delay due to a heat capacity. PA1 (c). Since the air flow rate measured by the H/W sensor contains pulsations produced by driving cylinders of an engine and also measuring noises, a lag filter is employed so as to eliminate these noises and pulsations. As a result of such a smoothing process, this smoothing process may cause a delay. PA1 (d). With respect to timings for performing a fuel injection, for instance, if the fuel injection would be performed based upon the air-flow rate when the measurement is made during the deceleration operation, the fuel injection by the injector would be completed, and therefore the air-flow rate at a time instance when air was mixed with the fuel and taken into the cylinder port would become greater than the air-flow rate at the measurement time instant. In other words, there is a difference between the air-flow rate at the measurement time instant and the air-flow rate at a time instant when an actual control is performed. PA1 (i). No method for precisely inferring or determining an air flow rate at a cylinder port has been established, and also been practically utilized. PA1 (ii). Even when such an air-flow rate at the cylinder port could be correctly grasped, the control characteristic of the air/fuel ratio is still deteriorated, because there are such problems that as described in the above-described problem (d), the air-flow rate is increased depending on the fuel injection timings, and also the fuel attached to the wall surface of the air intake manifold causes a delay in the fuel injected into the cylinder. PA1 (1). In an electronic engine controlling apparatus comprising means for detecting an engine revolution number, and means (air-flow rate meter) for detecting an air flow rate taken into the engine, there are provided means for calculating pressure at an air intake manifold and means for calculating an air-flow rate at a cylinder port; the pressure at the air intake manifold is calculated based upon the detected air-flow rate and the air-flow rate at the cylinder port which has been calculated by the means for calculating the air-flow rate at the cylinder port at one preceding measurement time instant; and an air-flow rate at the cylinder port at a present measurement time instant based on the engine revolution number and the calculated pressure at the air intake manifold. PA1 (2). In an electronic engine controlling apparatus comprising means for measuring a throttle valve opening angle, means for detecting an engine revolution number, and means for detecting an air-flow rate, there is provided means for predicting a value at a predetermined preceding time instant from a measured throttle valve angle; based upon the throttle valve angle predicted by the predicting means and also the engine revolution number detected by the engine revolution number detecting means, a shift between-the air-flow rate detected by the air-flow rate detecting means and the air-flow rate at the cylinder at said predetermined preceding time instant is inferred by way of a predetermined calculation; the detected air-flow rate is corrected by the shift; and the air-flow rate at the cylinder port at said predetermined preceding time instant is calculated.
As previously described, since there are problems in the control mechanism and measuring process at the engine control apparatus, the air-flow rate at the cylinder port could not be precisely detected during such a transition driving operation as the acceleration/deceleration.
To solve the above-described conventional problem (a), an air-flow rate Qe(n) at a cylinder port is calculated by the following equation (al): EQU Qe(n)=(1-K.sub.F)Qe(n-1)+K.sub.F Qa(n) (a1)
It has been proposed to calculate a fuel injection amount based upon the calculated air-flow rate so as to control the air/fuel ratio. It should be noted that symbol Qa(n) indicates an air-flow rate measured by an air-flow rate sensor and symbol "n" denotes a time instant in the above-described equation (al).
The above equation (al) has an aim to correct by way of a first order lag filter, a difference between an air-flow rate at a cylinder port and a measured air-flow rate when an air intake manifold is filled with air during, for instance, an acceleration operation. It should be noted that the coefficient "K.sub.F " of the equation (al) is determined by the engine revolution number and volume efficiency. Since several uncertified elements are involved when this coefficient K.sub.F is actually determined and furthermore the conventional problems (b) to (d) are still present, it is rather difficult to obtain such a coefficient K.sub.F for precisely and continuously controlling the air/fuel ratio even during the above-explained transition operation period. Also, there are similarly problems in the following equation (a2) where a fuel injection amount T.sub.p is subjected to the smoothing process: EQU T.sub.pe (n)=(1-K.sub.F)T.sub.pe (n-1)+K.sub.F T.sub.P (n) (a2)
where symbol "T.sub.pe indicates a fuel injection amount at a cylinder port.
On the other hand, with respect to the above-described problems (b) to (d), for instance, there has been proposed that the measured air-flow rate is subjection to a first order lead filter process so as to compensate these lags: EQU Qae(n)=Qa(n)+d{Qa(n)-Qa(n-1)} (a3)
In case that the measured lag in the air-flow rate as described in the above-described conventional problems (b) to (d) is compensated by performing the lead filtering process as defined in the equation (a3), the pulsations and measuring noises are contained in the measured air-flow rate. As a consequence, the noise application caused by the lead filtering process will be produced. When such a signal containing the noise is used as a fundamental signal for determining the fuel injection amount, there is another problem to cause fluctuation in the fuel injection. It should be noted that coefficient "d" expressed in the above equation (a3) may be determined by the sampling period and the like.
Furthermore, either the asynchronous injection amount, or the asynchronous injection pulse width is obtained, as described in the publication "Electronic Controlled Gasoline Injection" by Fujisawa et al., issued in July 1987 by Sankaido publisher, pages 116 to 117, by utilizing the throttle-valve-angle data and by retrieving the values of the memory map based upon the variation in the throttle valve opening angle data. According to this conventional technique, the variations in the throttle valve opening angles are subdivided into several levels, and thus the asynchronous injection amount is determined by recognizing to which acceleration level, the variations in the measured throttle value opening angle belong. However, this conventional technique does not correspond to a basic method for grasping a phenomenon, but rather to a so-called "symtomatic treatment", and has such a difficulty that a huge number of matching steps are necessarily required for the memory map.
Also, another conventional method for aiming prevention to these conventional problems (a) to (c) and of the air-flow rate sensor due to a cost reduction, has been described in, for example, JP-A-63-32144. In this conventional method, for normal or steady air-flow rate is obtained from the throttle valve angle and engine revolution number, and the lag processing operation is performed so as to detect the air-flow rate at the cylinder port. However, there are other problems with this conventional method in order to obtain the air-flow rate at the cylinder port in higher precision. That is to say, no only variations in pressure at the upper stream of the throttle valve must be considered, but also the temperature at the suction pressure, the air flow rate passing through the bypass tube, and EGR (Exhaust Gas Recirculation), namely air-flow rate while recirculating the exhaust gas must be taken into account. In addition thereto, the mounting precision of the throttle-valve-opening-angle sensor may give a great influence to the air/fuel ratio controlling characteristic, for instant, if the mounting positional error of the throttle valve angle sensor becomes 0.1.degree., then there are produced 4% errors in the air/fuel ratio.
As previously described, although many attempts have been made to correctly detect the air flow rate at the cylinder port, the conventional problems could not yet completely solved. It should also be noted that there is a change in a relationship between the air-flow rate passing through the throttle valve and the air-flow rate at the cylinder port in connection with variations in the ambient conditions.
Next, other conventional technical methods for solving the above-described problems (a)-(d), and their problems will now be described, in which the fuel injection amount has been corrected based upon the variations in the throttle valve opening angles, instead of correctly detecting the air flow rate at the cylinder port.
In prior art, since there are complex problems in the above described conventional problems (a) to (d) and the fuel supply delays caused when the injected fuel is attached to the air-intake wall surface, the corrections based upon the throttle valve angle capable of detecting the transition driving operation such as the acceleration/deceleration operations at first in order to correct the deterioration of the control characteristic for the air/fuel ratio. For instance, in the conventional fuel injection controlling method, when the engine is brought into the acceleration state, the fuel injection amount is corrected based upon the increase in the throttle valve opening angle. This correction is performed by increasing the fuel injection amount in response to the increase in the air-intake flow rate, depending upon the variations in the throttle valve opening angle, and by making the necessary adjustment on the basic fuel injection pulse width which is obtained by the air-intake flow rate or the pressure at the air intake manifold, and also the engine revolution number. Thus, the fuel is supplied in response to the fuel injection pulse to which other corrections have been added, based on other measurement data, e.g., water temperatures.
Then, the fuel supply is carried out in synchronism with the crank angle. As another method for correcting the acceleration operation, the asynchronous fuel injection in which the fuel is injected under the asynchronous condition with the crank angle has been performed. This asynchronous fuel injection can prevent the air/fuel ratio from becoming lean (e.g., condition that the fuel supply is not satisfied in order to allow the air-flow rate) in such a rapid acceleration mode that the sufficient fuel cannot be supplied in case of the synchronous fuel injection.
Another method for reducting a fuel injection amount based upon a variation in a throttle valve opening angle has been proposed during not only an acceleration state but also a deceleration state. This conventional correcting method is to prevent that the air/fuel ratio is enriched (i.e., condition that too much fuel is supplied for the air-flow rate) during the deceleration operation.
As previously described, the conventional techniques for correcting the fuel injection amount based upon the throttle valve opening angle, and also for matching various sorts of correction coefficients so as to improve the control characteristic of the air/fuel ratio, could be established under the recent exhaust gas controlling regulations.
It should be understood that in order to obtain the above-described throttle valve angle, there are many possibilities. That is to say, the throttle valve angle sensor is not employed, but either an acceleration pedal angle, or an acceleration pedal position may be detected to used as the throttle valve angle if the throttle is mechanically coupled to the acceleration pedal.
Furthermore, in accordance with the throttle controlling method in which the throttle is electronically coupled to the acceleration pedal, namely the acceleration pedal angles are employed as a major input, and then the throttle is controlled by the motor or the like, since the acceleration pedal angles have been measured, and the throttle valve angles may be easily calculated, this electronic throttle-valve-angle detecting method may be utilized.
Also, since the throttle-valve-angle signal has been utilized for various control apparatuses involving the engine control, as described below, this angle signal functions as an important control signal.
First, in the conventional engine control, the fuel injection control and injection timing control have been performed based upon the throttle-valve-angle signal. As a consequence, various correction methods have been established under such an initial condition that the throttle valve-opening-angle signal has been acquired.
Furthermore, in the automobile controls other than the engine control, there are transmission controls, traction controls and suspension controls as such controls for requiring the throttle valve opening angle. For instance, in the transmission control and the like a control is made in such a manner that a gear position is selected based upon the throttle valve angle and vehicle velocity, or the engine revolution number, and then the throttle-valve-angle signal per se functions as important information.
Originally, in order to improve the air/fuel ratio controlling characteristic, it has been understood that an air flow rate at a cylinder port during a transition driving condition should be detected or inferred. However, the following problems remain.
As previously described above, in accordance with the conventional fuel injection controlling methods, various corrections for the fuel injection amounts have been performed based on the throttle valve opening angle which corresponds to the most rapid information used when the transition driving operations, e.g., the acceleration/deceleration operations are carried out. There is another problem that the throttle valve angle sensor must be necessarily required in order to improve the air/fuel ratio controlling characteristic by way of the above explained conventional methods.
On the other hand, if such a throttle valve angle sensor is employed, the above-described other problems (i) and (ii) still remain.